Abstract: The heat exchange tube has a porous thermal shock resistant outer shell composed of a corrosion resistant ceramic material that may have a finned outer surface or a plain cylindrical outer surface. The outer shell contains an inner tube composed of a dense nonporous ceramic which is capable of containing high pressure gases, but which may not be as thermally shock resistant or corrosion resistant as the outer shell. The inner tube is formed of a dense ceramic material such as a highly dense silicon carbide or silicon nitride having at each end a like density insert. The end inserts provide sealing surfaces to contact other components in the heat exchanger such as identical ceramic tube assemblies to form a gas-type pressure seal. The inner tube can be fabricated by a deposition technique suh as a chemical or physical vapor deposition, and alternatively, can be made separately and press fitted into the outer shell or the outer shell can be cast or otherwise formed around the inner tube.